In conjunction with the operation of most internal combustion engines there are provided a variety of exhaust gas treating apparatuses or means. These devices by and large embody the purpose of protecting the atmosphere and the environment by treating the exhaust gas in such a manner to remove harmful components.
Such exhaust gas treating devices generally include a unit wherein the hot exhaust gases are received. The harmful components are therein filtered, oxidized, or eliminated through chemical reaction. Thus, as the treated exhaust gas leaves the filter it is relatively harmless, free of solid particles such as carbon which have been burned off, and can be safely discharged into the atmosphere.
Usually, exhaust gas filter, or smoke filters, as they are referred to, are so positioned with respect to the engine to receive the exhaust gas in as hot a condition as possible. Thus, although the exhaust gas as well as the exhaust gas path become heated, the temperature is not always sufficiently high to be effective in burning off carbon particles. This is found to be particularly true when the engine is operated for extended periods at idle or low load conditions.
In the instance of a filter which embodies a catalystic material, the hot exhaust stream is further increased in temperature within the catalyst bed passages. However, said temperature may still be too low to combust the carbon particles which are restrained in the bed.
In the regular operation of an exhaust gas treating unit, while the engine is idling the filter element will be at a low temperature and of little effect except to retain solid materials from the exhaust stream. However, at greater speeds or load conditions, the engine will soon discharge a relatively hot exhaust gas stream which, within a short period of time, can reach a temperature of about 700.degree. to 800.degree. at the discharge point. To be effective however in burning off carbon particles carried on the exhaust gas stream, the carbon particles should be elevated to a temperature of at least 900.degree. to 1200.degree. F. either in the gas stream or in the filter.
A further detriment experienced in the use of smoke filters designed for automotive applications is the increasing back pressure encountered within the filter. After a period of operation, such as circumstance can result due to the accumulation of carbon particles which tend to restrict and clog flow passages. The overall effect is to plug the filter and consequently decrease the engine's efficiency.
To overcome the above noted difficulties, the present arrangement includes in essence a smoke filter which is particularly adapted for treating and/or burning carbon particles which have been removed from an engine's exhaust gas stream. This is achieved by passing the exhaust stream, or a portion thereof through either a catalytic or a noncatalytic bed. Solid particles will thereby be removed from the stream and retained on the surface of the filter element.
The exhaust gas stream, as well as the particle retaining bed, are initially hot as the stream enters the filter. However, the filter bed is periodically heated by electrical means to a temperature sufficiently high to burn off the retained carbon particles.
An object of the invention therefore is to provide a smoke filter capable of cooperating with an internal combustion engine to treat exhaust gases leaving the latter. A further object is to provide an exhaust gas treatment unit capable of heating the bed of a smoke filter whereby carbon particles which have been removed from the exhaust stream will be readily combusted. Another object is to provide a smoke filter structure which will minimize filter back pressure during engine operation by keeping internal passages relatively clear of carbon particle accumulations.